1. Field of the Invention
This invention pertains to servomotors and servomechanisms generally, and in one facet, to throttle position sensors integrated with throttle actuator motors.
2. Description of the Related Art
For many years, man has relied upon motors to assist in various work functions. With the advent of more advanced electrical and electronic circuits, motors have been controlled by these circuits to improve efficiencies, provide precision placements or timings, and perform other various monitoring and control functions. Motor control has enabled man to use motors in applications beyond those strictly requiring great force or enduring power.
Motors today are used for positioning with more precision in space or time than obtainable with hand manipulation, and in environments which are inhospitable to human presence. These motors, commonly referred to as servomotors, form a part of a servomechanism. The control of the servomotor is often derived from a sensor directly attached to the motor, and may also be derived from other remote sensors. The servomotor may include a rotary, linear or other type of motor, depending upon the requirements of each specific application.
Machines as complex as most transportation vehicles today have many applications for servomechanisms. One specific application involves the control of internal combustion engine throttle. Control of throttle in passenger cars and trucks is usually dependent upon the position of an accelerator pedal, which represents vehicle operator demand. The accelerator pedal position, or demand, is then linked to the engine throttle. Accelerator pedal movement was transmitted for many years through mechanical linkages consisting of solid rods and ball joints. In some applications, the solid rod linkage was replaced by a cable within a sleeve, referred to in the trade as a Bowden cable. These mechanical linkages are prone to problems which tend to affect all mechanical systems, such as sticking, freezing, breakage, and other mishaps. In addition, adaptation of the mechanical linkages to allow for special features such as more efficient energy utilization, reduced emissions, idle speed control, and "limp-home" modes of operation are generally not practical, or even possible in some cases.
By using a sensor to sense accelerator demand, a servomotor to control the throttle position, and a computer system to control operation of the throttle relative to the input from the accelerator pedal sensor and other various sensed inputs, a variety of special features may be incorporated into the accelerator-throttle linkage. In these computer-assisted systems, the throttle linkage is commonly referred to as a "drive-by-wire" system, since the linkage is electrical.
The servomechanism becomes a remote control system, since a vehicle operator within a climate controlled passenger compartment controls a throttle located in the harsh climate of an engine compartment. In fact, remote control is a very common use for servomechanisms. The control of functions ranging from TV and radio tuners to space shuttle door releases and valve controls all are remote control applications. Once again, the desire for remote control may stem from precision in timing or positioning achievable from the servomechanism, or from the need to control a function in a harsh environment where human interventions may not be practical.
Each of these applications require a motor, and also a sensor to sense the position of the motor. A number of schemes have been devised for coupling the sensor to the motor, including magnetic coupling, where the sensor detects the magnetic flux produced by certain section of the armature optical coupling, where a toothed wheel breaks a passage of light or a reflective surface reflects the light during rotation; mechanical coupling, where the motor armature is used to directly drive the sensor or drive the sensor through such mechanical devices as gears, and other known methods. Each of these different coupling methods has benefit in specific applications.
In addition to coupling the sensor and the motor, the sensor must also be physically positioned relative to the motor. Direct integration between the motor stator, also sometimes referred to as the field winding, and the sensor is desirable, since parts counts are reduced and common functions may be removed to avoid duplication and reduce cost. In the prior art, direct integration often involved the placement of an open frame sensor, often of the resistive or magnetic field sensing type, directly within a servomotor housing designed to contain both the motor and the sensor. The relatively light weight sensor is easily carried within the more rugged motor housing, and the housing does not need to be duplicated for both components. Unfortunately, in this type of prior art servomotor, the sensor is exposed to contaminants from the motor which are adverse to the life and reliability of the sensor. In addition, less control is available over the contactor, paint and lubricant. All three must be carefully controlled to ensure long life and reliability of the sensor. For example, a sensor designed to operate through tens or hundreds of millions of cycles will fail after only a few million cycles if the contactor is bent. In addition, the motor may be destroyed if some part of the sensor should detach, flow or bend and interfere with motor movement.
An alternative prior art design combines a fully housed, assembled and tested sensor with a similarly housed and assembled motor. The sensor is merely driven from the motor shaft, with no other interaction between the two components. This design eliminates any concerns about contamination of the sensor or motor. Unfortunately, the parts which must be handled, inventoried, and serviced is also greater, as is the cost of the components. Furthermore, the fully housed sensor of the prior art generally includes a separate set of bearings from the motor, leading to potential axial misalignment of bearings, which will result in early failure of the sensor bearings. In fact, proper axial alignment is very crucial to the longevity of a servomotor.